The Wii version is nowhere near as nonlinear as the 360 version. You can't free roam the mall whenever you want, the zombie count is down, and some things are much more difficult to unlock in the Wii version than they were in the 360 version (like the Mega Buster). There is, however, a good amount of replay value, and I didn't find the smaller number of zombies to be an issue. You should definitely rent it first, then decide on buying it.

This game it's great, I played the xbox360 version and unless the graphics, I think the Wii version is far superior. The gameplay is better is like RE4 plus you can use anything in the mall to use as a weapon, is so fun and the aditional feature modes are great too.
If you have iron eyes you can compare the graphics of both versions and it's a litte difference, only becose the xbox360 can put more zombies doesn't mean every zombie on the Wii is easy beaten.